Emission material reflecting other emissions
The reason the effect is more noticeable with the yellow is due to how the colors are made up of components of Red, Green, Blue in conjunction with the high strength of the emission. The Red is pure red, the Green is pure green, while the Yellow is a mix of red and green. Since your emission is high (10) the rendered pixels in the camera will be truncated to an upper limit of 1.0. So for the Red LED the pixels will be around RGB values of (10,0,0), the Yellow (10,10,0) and the Green (0,10,0) and these are truncated to become Red (1,0,0), Yellow (1,1,0), Green (0,1,0). Adding in the reflection from the Yellow LED on the Red LED (assuming, say, 10% reflection) you'll get (11,1, 0) which will become (1,1,0) (yellow). The Red reflecting on the Yellow will be (11, 10,0) which will become (1,1,0). The Yellow reflecting on the Green will become (1,11,0) which will become (1,1,0) when values above 1.0 are clipped. ie, so Red + Yellow reflection becomes yellow, Yellow + Red reflection becomes yellow, Yellow + Green reflection becomes yellow - so it appears that there is no reflection of the Red and Green LEDs as they are 'lost' in the saturated yellow emission.

That's essentially what I believe is happening here. I don't think I've explained that too well - hope it makes sense.

I think this would actually be similar to how this would behave in the real world - although less pronounced since the human eye has a wide band sensitivity to light rather than the strict narrow banding in Blender's RGB model.